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BLEACHING POWDER (CHLORIDE OF LIME)            55

(2) 200 c.c. of the baryta solution are treated in a 250 c.c. flask with
a little cadmium carbonate suspended in water and heated for about 30
minutes on a steam-bath with frequent shaking. On cooling, the liquid
is made up to 250 c.c. and filtered through a dry paper, 200 c.c. of the fil-
trate, acidified with acetic acid, being titrated with iodine in presence of
starch paste.

The first titration gives the iodine consumed by the sulphides and
thiosulphates and the second that consumed by the thiosulphates alone;
it is easy, therefore, to deduce the thiosulphuric acid and hydrogen sulphide,
which are calculated as barium salts.

(c) Other determinations. Commercial baryta does not usually contain
lime and free alkali in appreciable quantity; otherwise the volumetric
determination of the baryta gives inaccurate results.

The presence of other bases is readily detected indirectly, by determining
the barium in 25 c.c. of the aqueous solution—prepared as above—gravi-
metrically as sulphate and calculating it as crystallised barium hydroxide.
If this result is lower than that obtained volumetrically, the latter must
be erroneous owing to the presence of other bases.

BLEACHING  POWDER

(Chloride of Lime)
CaOCl3 = 127

White, hygroscopic powder with an odour of chlorine, partially soluble
in water and soluble in hydrochloric acid with evolution of chlorine. The
commercial value depends on the content of available chlorine. That to
be used for bleaching textiles should be tested for iron and manganese.

Determination of the Available Chlorine (Penot and Lunge's
method).—10 grams are well pounded in a mortar with a little water, further
quantities of water being gradually added with constant mixing. The
whole of the liquid and solid matter is introduced into a litre measuring,
flask and made up to the mark and mixed, 50 c.c. of the turbid liquid being
immediately removed. Into this liquid standard sodium arsenite x is run
slowly from a burette with gentle shaking until a drop of the solution no
longer colours starch-iodide paper.2 The end-point is easily fixed, since
the coloration of the paper gradually weakens beforehand.

The number of c.c. of arsenite used, multiplied by 2, gives the number
of litres of chlorine (at o° and 760 mm.) per kilo of substance. This repre-
sents the chlorometric degree, Gay-Lussac degree or French degree of the
chloride. To obtain the percentage of chlorine by weight (English, German,
American degree], the chlorometric degree must be multiplied by 0-31698.

1  4-425 grams of arsenicras acid (puriss.) and 13 grams of crystallised sodium car-
bonate (ptiriss.) are dissolved in hot water and the volume made up to i litre after
cooling.

2  3 grams of pure potato starch are mixed with 250 c.c, of cold water and boiled with
constant stirring ;  2 grams of pure potassium iodide and i gram of crystallised sodium
carbonate are added and the volume made up to 500 c.c.    Strips of filter-paper, after
immersion in this liquid, are allowed to dry and kept in well closed vessels.of ethyl acetate in 100 c.c. of the amyl acetate